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Incidence of lung cancer greater among young women
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Age-specific incidence of lung cancer decreased among both men and women aged 30 to 54 years across all races and ethnicities, according to results of a study published in The New England Journal of Medicine.
However, declines were larger among men, indicating a reversal in the historically higher incidence of lung cancer among men compared with non-Hispanic white and Hispanic women born since the mid-1960s.
“This finding ... may foreshadow a higher future burden of overall lung cancer among women than among men as younger cohorts age, which further underscores the need to intensify antitobacco measures to decrease smoking among young women,” Ahmedin Jemal, DVM, PhD, vice president of the Surveillance and Health Services Research Program at American Cancer Society, and colleagues wrote. “Our finding also calls for continued monitoring of sex-specific risks of lung cancer and for etiologic studies, including studies of sex differences in smoking-related susceptibility to lung cancer, to identify reasons for the higher rates of lung cancer among young women.”
Historically, women have been less likely to smoke, began smoking at older ages and smoked fewer cigarettes per day than men. However, research has indicated that men and women increasingly exhibited similar smoking behaviors.
Jemal and colleagues used the North American Association of Central Cancer Registries to determine the prevalence of smoking from 1970 to 2016 and the incidence of lung cancer diagnoses from 1995 to 2014 based on sex, race and ethnicity, age group, and calendar year of diagnosis. Researchers sought to determine whether incidence of lung cancer was higher among women than men and whether patterns in smoking behaviors accounted for this difference.
Investigators used SEER software to estimate age-specific incidence of lung cancer per 100,000 person-years and the Tiwari method to estimate the female-to-male incidence ratio.
Overall incidence of lung cancer decreased among both men and women, but the decrease appeared greater among men. Among non-Hispanic whites, the female-to-male incidence rate ratios increased to more than 1 among all individuals except those aged 50 to 54 years.
Among individuals aged 40 to 44 years, the incidence rate ratio increased from 0.82 (95% CI, 0.79-0.85) for 1995-1999 to 1.13 (95% CI, 1.08-1.18) for 2010-2014.
Incidence rates among men generally decreased with each birth cohort, whereas rates among women increased in the cohorts born around 1950 to around 1960, and decreased thereafter.
Thus, the incidence rate for those aged 45 to 49 years was 27 per 100,000 person-years among women and 36.5 per 100,000 person-years among men born in 1950, which resulted in a female-to-male incidence rate ratio of 0.74 (95% CI, 0.72-0.76). The incidence rate ratio was 24.9 per 100,000 person-years among women and 23.1 per 100,000 person-years among men for those born around 1965, which resulted in a female-to-male incidence rate ratio of 1.08 (95% CI, 1.05-1.11).
Researchers observed the highest incidence among women who were white or Hispanic.
Among white individuals aged 40 to 44 years, the female-to-male incidence rate ratio increased from 0.88 (95% CI, 0.84-0.92) in 1995-1999 to 1.17 (95% CI, 1.11-1.23) in 2010-2014. Hispanics in the same age group had a ratio that increased from 0.79 (95% CI, 0.67-0.92) to 1.22 (95% CI, 1.04-1.44) during the same period.
Sex-specific incidence rates converged among Hispanics, non-Hispanic Asians, non-Hispanic blacks and Pacific Islanders but crossed over only in the Hispanic population.
Although men historically had higher smoking rates, the difference in prevalence became progressively smaller for each younger birth cohort because of the convergence of initiation rates and lower cessation rates among women.
Sex differences among whites disappeared among those born during the 1960s and afterward, and prevalence was minimally higher among women aged 40 to 49 years born around 1965. Smoking behaviors appeared generally similar among blacks and Hispanics, with the female-to-male ratio of smoking prevalence peaking among those born during the 1960s and declining thereafter.
“We do not believe sex differences in smoking behavior explain our finding of a gender crossover,” Jemal said in a press release. “For example, the crossover also occurred among Hispanics, even though smoking continues to be less common in young Hispanic women than young Hispanic men.”
“The patterns of historically higher incidence rates of lung cancer among men than among women have reversed among non-Hispanic whites and Hispanics born since the mid-1960s, and they are not fully explained by sex differences in smoking behaviors,” the researchers added. “Future studies are needed to identify reasons for the higher incidence of lung cancer among young women.” – by Melinda Stevens
Disclosure s : Jemal reports no relevant financial disclosures. Please see the study for a list of all other authors’ relevant financial disclosures.
Perspective
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Every day, we are seeing more young women in the lung cancer clinics. The findings from Jemal and colleagues have confirmed our concerns. The incidence of lung cancer is changing. Today, more young women (aged 30 to 54 years) are being affected by lung cancer than young men.
The observations were reported across non-Hispanics whites and Hispanics, suggesting that more than sociocultural factors are influencing these patterns. Multiple studies have described the “delayed smoking phenomenon,” which refers to women starting to smoke 2 to 3 decades after men, with a subsequent increase in lung cancer cases. Although this could explain some of the lung cancer cases seen in the 1980s or 1990s, the prevalence of cigarette smoking among women has not generally exceeded men.
Many questions remain unanswered, from risk factors only affecting women to the effect of sex hormones in lung cancer. One of the most pressing questions is: Are we ready to treat or accommodate the needs of women with lung cancer? Most of the data regarding supportive care comes from breast cancer, and it is unclear if they can be extrapolated to patients with lung cancer. In addition, what are the effects of immune checkpoint inhibitors on fertility?
Further research is necessary to understand the reason for this increased incidence and the effects of treatment on women with lung cancer. We conducted a study about sex differences in tolerability to immune checkpoint inhibitors. We observed women were more likely to develop immune-related adverse events. This supports what has been described for many decades: the immune systems of men and women are different. Women mount stronger innate and adaptive immune responses, and they force tumors into a more extensive self-editing process before they can escape immune system.
Perceptions also would need to change. Lung cancer is no longer — if it ever was — a disease of men. We need to continue to study lung cancer among women with the hope of improving outcomes and survivorship.
Lastly, over recent years, many lung cancer advocacy groups have focused on supporting women with lung cancer. Most of them are easily found on social media. Connecting with advocates will help us understand their needs and support their efforts to improve funding for studying lung cancer among women.
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